The NVIDIA GeForce GTX 660 Ti 2GB graphics card features a 915MHz base clock, 980MHz boost clock, and 1.5GHz GDDR5 video memory. The GeForce GTX 660 Ti is built on the "GK104" core -- the same as the GeForce GTX 670 graphics card -- and features 1344 Stream/CUDA processors, 7 SMs, 4 GPCs, 7 tesselation units, 24 ROPs, and a transistor count of around 3.54 billion. The recommended retail price at launch for the NVIDIA GTX 660 Ti is $299 USD.
Early reviews of the NVIDIA GeForce GTX 660 Ti are fairly positive, at least under Windows. Some of the 660 Ti reviews that were published today can be found via the OpenBenchmarking.org Cekora Engine.
If you were hoping for some Linux benchmarks of the GeForce GTX 660 Ti today, unfortunately there aren't any on Phoronix or from any other major source. NVIDIA PR really isn't interested in Linux.
If you're curious about the NVIDIA GeForce 600 "Kepler" series support in general, see my GeForce GTX 680 Linux review of the graphics card that was kindly sent over by NVIDIA's Linux/Unix team. There's also my GTX 680 Windows 7 vs. Ubuntu 12.04 comparison.
As of the current driver support for the Kepler hardware on Linux, the NVIDIA binary driver is in good shape with the many recent advancements. The only main feature lacking from the binary Linux graphics driver is that there isn't any CoolBits overclocking support for any Fermi/Kepler GPUs although the Windows driver does provide this overclocking ability. In addition there's some other minor feature differences like no support for the new TXAA anti-aliasing mode and other features at this time.
In terms of the Nouveau Kepler support, they surprisingly managed some same-day support. There's basic open-source OpenGL support via the recent Nouveau Gallium3D and DRM/KMS components, but it's not in good shape. First of all, for any accelerated support, one must extract the Kepler microcode for their graphics card by first initializing the hardware with the binary driver. Extracting your own FUC microcode for Kepler is needed until the Nouveau DRM driver can generate it on its own, which at the soonest point would be the Linux 3.7 kernel (there's been no code for this yet).
Even after getting the acceleration support for Nouveau Kepler, re-clocking isn't yet working so the clock speeds for the core, shaders, and memory are very low -- thus leading to very slow performance. Without the proper re-clocking support and other power management work, the power consumption is also disappointing.
Basically if you want to use any NVIDIA GeForce 600 series graphics card under Linux right now, you should be using the binary driver from NVIDIA.com. In the coming months the open-source Nouveau driver support will be improved, but it's in a less than ideal state right now. If you want open-source NVIDIA graphics, I'd recommend going with a GeForce 200/300 series graphics card -- or something even older -- for the best and most feature-rich experience on Nouveau.